The invention relates to a method of manufacturing a cable in which one or more electrical and/or optical conductors are surrounded entirely or partly by supporting elements. The supporting elements are made of a synthetic resin, and they extend over the whole length of the cable. The supporting elements and the conductors are covered with a cable sheath.
The invention further relates to a cable manufactured according to this method, in particular an optical cable.
German Offenlegungsschrift No. 3,112,422 describes the use of so-called filling elements in the core of the cable in addition to the conductors, in this case optical light conductors. The filling elements are provided to give the core of the cable a cross-section which is as circular as possible. The filling elements may be, for example, a synthetic resin.
A cable which has a synthetic resin central core is described in German Offenlegungsschrift No. 3,133,695 (corresponding to British Patent Application No. 2,082,790). The core is provided with longitudinal grooves in which the conductors are provided. A synthetic resin sheath is shrunk around the core and the conductors.
A disadvantage of these known cables is that the synthetic resin supporting elements, for example filling elements or central inserts, are subject to shrinkage during heating of the cable. Such shrinkage affects both the mechanical properties of the cables and the transmission properties of the optical fibers.
For example, a mixed armoured cable, which in addition to synthetic resin supporting elements also comprises tension-proof non-shrinking elements, may fail when the cable is subjected to high temperatures. As a result of the shrinkage of the supporting elements upon cooling of the cable, the tension-proof elements will open or warp and provide an extra load on the cable sheath present over the armour.
In optical cables the shrinkage of the supporting elements, which together with the optical conductors (fibers) may be provided in the cable core, increases an optional overlength of the fibers in the cable so that as a result the optical transmission properties of the cable are changed uncontrollably.